Piping systems for distributing high pressure and temperature fluids are generally designed to provide some degree of flexibility to allow for dimensional tolerances, thermal expansion and contraction, and vibrational or structural deflections between the various components which are connected by the piping. For example, ducting systems are used in aircraft for distributing high pressure air tapped from the turbine engine compressors to environmental (pressure and temperature) controls in aircraft cabins, wing and nacelle leading edge de-icing systems and numerous other pneumatic systems.
Lightweight compact assemblies, which are particularly desirable in aircraft and missile systems, for providing such flexibility are known in the prior art. However, some of these prior art devices employ elastomeric, plastic, rubber or asbestos type seals to prevent leakage of the fluid flowing in the flexible system. A shortcoming of these types of seals is that they tend to fail when exposed to high temperatures above approximately 400.degree. F.-500.degree. F., very low temperatures, or radiation.
Other sealing assemblies used in flexible piping systems in environments beyond the capability of elastomeric seals and the like employ sections of piping with circumferential corrugations, i.e., bellows, expansion loops, or devices containing piston rings. Such hermetically-sealed flexible joints are known as bellows-sealed ball and gimbal joints. However, these joints or sealing systems are generally very heavy, require large amounts of space, and are prone to failure and, therefore, leakage, due to fragility and wear. Moreover, these joints or sealing systems often require exact tolerances and are difficult to manufacture and install.
In certain cases, there is insufficient space in ducting system installations to accommodate the length of presently available metallic bellows-sealed flexible joints. There may also be a need for a flexible joint with a rotational degree of freedom, which cannot be obtained by using a joint comprising a metallic bellows seal.
Solving these problems, it is known to utilize metal to metal seals in such an environment as disclosed in prior U.S. Pat. Nos. 4,054,306 to Sadoff et al; 4,071,268 to Halling et al and 4,071,269 to Halling et al. At higher temperatures, above for example 900.degree. F., the seals disclosed in these patents perform extremely satisfactorily and leakage of fluid is minimal. This is because while a rubbing action of the two metallic parts, which are in sliding contact, tends to gall the contacting parts, an oxide film is continuously formed, maintaining a lubricous, non-galling surface. However, it has been noted that at more moderate temperatures this oxide film does not regenerate, and thus galling tends to roughen the metallic surfaces, thereby increasing the chance of leakage of fluid between them.
In addition to maintaining the seal between joined pipes, it is important to provide a mechanism that allows for rotation and angulation between adjacent pipes. Earlier non-bellows flexible joints, such as those shown in U.S. Pat. Nos. 4,071,269 to Halling et al and 4,448,449 to Halling, et al, provided all degrees of freedom, including rotational freedom but had little advantage over bellows-sealed joints in terms of length. Joints produced by others that had the capability of rotational freedom and could have been made shorter, suffered from high leakage due to the absence of pressure-energization and from rapid wear of their sealing elements. Moreover, the position of their seals and the unsuitability of their materials make these joints unsuitable for long term service in high vibration environment at high temperatures and pressures. Examples of such joints are shown in U.S. Pat. No. 4,427,220 to Decker.
Other examples of such prior art devices are disclosed in the following U.S. Pat. Nos. 1,155,495 to Leake; 2,005,556 to Parker; 2,451,437 to Fenlon; 2,502,753 to Rohr; 2,840,394 to Rohr; 2,846,242 to Drake; 3,033,595 to Bard; 3,165,339 to Faccou; 3,663,043 to Walton; 3,656,784 to Dow et al; 3,799,586 to Caras et al; 3,995,896 to Decker; 4,006,881 to Gaillard; and 4,165,107 to Affa et al. These prior art flexible joints, including bellows-sealed joints, do not combine the necessary capabilities for use in tight spaces which requires a light and compact joint arrangement.
In view of the above, there exists a need in the art for a flexible joint which is short in longitudinal length and can provide sufficient angular and rotational movements for installation in small spaces. This invention addresses this need in the art, as well as other needs which will become apparent to those skilled in the art once given this disclosure.